Chap, v.] the Influence of the History of Development. 18 



Though these words might not contain a theory of descent 

 capable at once of scientific application, yet they show that 

 the latest researches and candid appreciation of facts were 

 compelling the most eminent representatives of the botany 

 of the day to give up the constancy of forms. At the same 

 time in the genetic morphology which had developed itself 

 mainly under Nageli's guidance since 1844, and still more in 

 embryology, which in Hofmeister's hands was leading to results 

 of the greatest systematic importance, there lay a fruitful 

 element destined to correct and enrich Darwin's doctrine of 

 descent in one essential point. That doctrine in its original 

 form sought to show that selection, the result of the struggle 

 for existence, combined with perpetual variation was the sole 

 cause of progressive improvement in organic forms l ; but 

 Nageli, relying on the results of German morphology, was able 

 as early as 1865 to point out that this explanation was not 

 satisfactory, because it leaves unnoticed certain morphological 

 relations, especially between the large divisions of the vege- 

 table kingdom, which scarcely seem explainable by mere 

 selection in breeding. While Nageli allowed that Darwin's 

 principle of selection was well adapted to explain fully the 

 adaptation of organisms to their environment and the 

 suitableness and physiological peculiarities of their structure, 

 he pointed out that in the nature of plants themselves there 

 are intimations of laws of variation, which lead to a perfecting 

 of organic forms and to their progressive differentiation, in- 

 dependently of the struggle for existence and of natural 

 selection ; the importance of this result of morphological 

 research has since been recognised by Darwin. Thus Nageli 

 supplied what was wanting in the theory of descent and gave 

 it the form in which it is adequate to explain the problem 

 already recognised by the systematists of the old persuasion, 



1 See Darwin's repudiation of this statement on p. 421 of Ed. 6 of the 

 1 Origin of Species.' 



